Brighteners and process for cyanide zinc electrodeposition



United States Patent 3,274,080 BRIGHTENERS AND PROCESS FOR CYANIDE ZINC ELECTRODEPOSITION Robert E. Harrover, Jr., North Huntingdon Township,

Westmoreland County, Pa., assignor, by mesne assignments, to Cowles Chemical Company, Shaker Heights, Ohio, a corporation of Ohio No Drawing. Filed May 25, 1962, Ser. No. 197,598

17 Claims. (Cl. 204--55) This invention relates to bright zinc electroplating methods, novel brightener addition compositions and novel electrolyte compositions.

The typical electrodeposits from an aqueous cyanide zinc electrolyte are dull and granular. Numerous attempts have been made by those working in the art to improve the character of zinc deposits obtained from aqueous alkaline cyanide baths. Many addition agents have been used and some progress has been made. Nonetheless, electrodeposits of zinc from aqueous cyanide plating baths typically lack one or more desirable properties such as brightness, grain refinement and attractive color, or for example the bath may lack good throwing power.

Accordingly, it is the general object of this invention to provide novel brightener addition agents or compositions, novel aqueous alkaline cyanide zinc electrolyte compositions with good throwing power and plating methods which will enable the attainment of bright, fine grained and attractive zinc deposits.

It is a more particular object of this invention to provide a particular combination of additives which can be effectively employed in an aqueous alkaline cyanide zinc bath to produce superior bright, ductile Zinc coatings.

A further object of this invention is to provide novel electrolyte compositions which will produce superior bright, fine grained, smooth Zinc coatings and which exhibit excellent throwing power so that a uniform bright zinc coating may be deposited on irregularly shaped and recessed objects.

Still another object of this invention is to provide a zinc electrodeposit which responds in an excellent manner to clear conversion coatings and dilute oxidizing bright dips.

Briefly, the present invention accomplishes the above cited objects by providing a class of compounds which provide a beneficial effect on the brightness and color of zinc electrodeposits when employed in an aqueous alkaline zinc cyanide electrolyte. Moreover, these compounds and others, when employed in combination with polyvinyl alcohol, exert a profound and synergistic effect upon the brightness, color and smoothness of the resulting zinc plate.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

It has now been found that a particular class of compounds can be used to produce an improved zinc electrodeposit from aqueous alkaline cyanide electrolytes. When added to an aqueous alkaline zinc cyanide electrolyte, at least one brightener compound selected from the group consisting of compounds having the formulas:

where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of NH -OH and COOR said R is selected from the group consisting of H, NH, and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH CH NH (CH NH Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, will produce an electrodeposit with improved brightness and grain size, especially at low current densities, as for example /2 to about 15 ampere/ft? These compounds may be incorporated into aqueous alkaline cyanide zinc plating baths as illustrated by the following specific examples, with the indicated results.

Example I Oz./ gal. Zinc oxide 5.6 Sodium cyanide 12.3 Sodium hydroxide 5.0 Tetraethylthiuram disulfide 0.02

Zinc may be electrodeposited from this electrolyte with an improvement in the brightness of the deposit, particularly in the range of /2 to 15 amperes/ft Example 11 OZ./ gal. Zinc oxide 5.6 Sodium cyanide 10.5 Sodium hydroxide 3.4

Dibutyldiethylthiuramdisulfide 0.006

Zinc may be electrodeposited from this electrolyte with an improvement in the brightness and grain size of the deposit.

Example 111 Oz./gal. Zinc oxide 5.6 Sodium cyanide 12.3 Sodium hydroxide 5.0 Trimethyl-N-acetic acid thiuram disulfide 0.01

Zinc may be electrodeposited from this electrolyte with an improvement in the brightness of the deposit, particularly in the range of 1 to 10 amperes/ft Example IV Oz./gal. Zinc oxide 5.0 Sodium cyanide 12.0 Sodium hydroxide 5 .0 Trimethyl-N-sodiurn acetate thiuram disulfide 0.03

Zinc may be electrodeposited from this electrolyte with an improvement in the brightness of the deposit, particularly in the range of /2 to 18 amperes/ft.

Example V 02/ gal. Zinc oxide 5.6 Sodium cyanide 12.3 Sodium hydroxide 5.0

Trimethyl N ammonium acetate thiuram disulfide 0.003

Zinc may be electrodeposited from this electrolyte with a visible improvement in brightness and grain size.

Example VI Oz./gal. Zinc oxide 5.6

Sodium cyanide 12.3 Sodium hydroxide 5.0

Zinc dimethyldithiocarbamate 0.05

Zinc may be electrodeposited from this electrolyte with a significant improvement in brightness and grain size.

Example VII Zinc may be electrodeposited from this electrolyte with an improvement in the brightness and grain size of the deposit, particularly in the range of A2 to amperes/ft.

Example VIII 7 Oz./ gal. Zinc oxide 5.6 Sodium cyanide 12.3 Sodium hydroxide 5.0

Sodium methyl-N-sodium acetate dithiocarbamate 0.008

Zinc may be electrodeposited from this electrolyte with an improvement in the brightness and grain size of the deposit, particularly in the range of /2 to 10 amperes/ft.

It is to be understood that the foregoing examples are only illustrative and that other compounds within the class defined by the structural formulas presented hereinabove may be employed according to this invention. For example, potassium, calcium, magnesium, cadmium, cobalt, molybdenum and manganese compounds may be substituted for the zinc, nickel and sodium compounds of the foregoing specific examples, with equivalent results.

The compounds may be employed in concentrations limited only by their solubility in the aqueous alkaline zinc cyanide bath. However, it is preferred to maintain the concentration in a range of from about 0.003 to about 0.02 oz./ gal. for optimum results.

The use of polyvinyl alcohol as a brightener addition agent for zinc cyanide plating baths is known and has been so described in the prior art. However, it has now been discovered that when polyvinyl alcohol is employed in combination with at least one of any of the compounds described heretofore, hereinafter referred to as dithiocarbamate compounds, a profound effect on the brightness of the zinc deposit is produced. The combination also surprisingly increases the throwing power of the bath so that uniform bright zinc coatings may be deposited on irregularly shaped and recessed objects. The combination produces a much brighter, more uniform zinc deposit over a Wider current density range than when either material is used alone.

Also known and described in the art as brightener addition agents for zinc cyanide plating baths are the reaction products obtained by reacting substantially equimolar quantities of at least one compound having the nucleus H I ll with ammonia or certain derivatives thereof as will be described more fully hereinbelow. The preparation of these reaction products, among others, are described in US. Patent 3,018,232, assigned to the assignee of this invention.

It has been discovered that when at least one of the reaction products described hereinbelow is employed in combination with polyvinyl alcohol, a profound effect on the brightness and grain refinement of the zinc is produced, similar to the effect of employing polyvinyl alcohol in combination with the described dithiocarbamate compounds.

Examples of compounds having the nucleus CN-C- t t t for the purposes of this invention, are 2-thiohydantoin and substitution derivatives of 2-thiohydantoin having at least one organic substituent in the 1, 5 positions. The nucleus of these 2-thiohydantoin substitution derivatives has the following structure:

Various organic radicals may be substituted at one or both of the 1 or 5 positions, providing the compound obtained upon reaction with ammonia or derivatives thereof is soluble in the aqueous alkaline cyanide zinc electrolyte in an amount sufficient to produce an appreciable improvement in brightness and smoothness of the zinc deposited. Examples of suitable compounds are:

Z-thiohydantoin l-acetyl-Z-thiohydantoin 5 (Z-hydroxylbenzal)2-thiohydantoin 5-furfural-Z-thiohydantoin 5-benzal-2-thiohydantoin l-methyl-Z-thiohydantoin Other examples of compounds having the nucleus CNC ll 1 ll 0 H s which are suitable for reaction with ammonia or derivatives thereof to produce the reaction products employed in this invention include:

Z-thiobarbituric acid 1-acetyl-Z-thiobarbituric acid 1-benzoyl-2-thiobarbituric acid 1,S-diacetyl-Z-thiobarbituric acid 2-thiopyrrolidone-4 5-thio-1,2,4-trazolidinone-3 4-thiooxazolidin0ne-4 4-thiothiazolidinone-4 3-thio-1,2,4-oxadiazolidinone-5 3-thio-l,2,4-thiadiozolidinone-5 2-thioazolidinone-6 2-thio-1,3-diazolidinone-4 2-thio-1,4-diazolidinone-6 3-thio-1,2,4-triazolidinone-5 2-thio-1,3,5-triazolidinone-4 5-thio-1,2,4-triazolidinone-3 1-thio-2-benzazolone-3 3-thio-2-benzazolone-1 Reaction products suitable for use in this invention, may be produced by reacting the compounds having the nucleus CNC II I II 0 H s heretofore described, with compounds having the formula wherein R is a radical selected from the group consisting of hydrogen; monovalent and divalent saturated substituted and unsubstituted aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms in which the substituents are selected from the group consisting of NH and OH radicals, phenyl radicals, monovalent and divalent alicyclic radicals containing from 5 to 6 carbon atoms in the ring in which the substituents are selected from the group consisting of CH -NH and OH radicals and amin ophenyl radicals.

Specific examples of the amine compounds included within the scope of the terms identified above include:

ammonia isopropylamine monoethanolamine ethylenediamine dibutylamine methylethylolamine diisopropanolamine methyl-propylenediamine diethylenediamine propylolmethylenediamine cyclopentylamine dicyclohexylamine cyclopentylmethylamine cyclohexylisopropylolamine cyclopentylethylenediannne 3 -methylcyclohexylamine 1,2-diaminocyclopentane 4-hydroxycyclohexylamine aniline p-aminoaniline methylani-line ethyl-4-methylcyclohexylamine 4-methylaminocyclohexylarnine 1-methylamino-2-hydroxycyclopentane p-aminomethylaniline cyclohexylaniline diphenylamine 2-methylhexylethylolamine N-ethylolaniline phenyl-4-aminocyclohexylamine N-ethylol-p-aminoaniline 4-methylcyclohexylpropylenediamine dimethylcyclohexylamine phenylethylenediamine di-4-aminocyclohexylarnine N-cyclopentylaminoaniline 3-isopropy-lolaminocyclohexanol ethylol-1,4-diaminocyclohexane phenylcyclohexanolamine phenyl-p-aminoaniline N-(2'-arninoethylene)-l ,4-diaminocyclohexane N- 2 aminoisopropylene) -4-aminocyclohexauol N- cyclopentyl-l,4-diaminocyclohexane cyclohexylmethylcyclohexyl-amine dip-aminophenylamine p-aminophenyl-4-methylcyclohexylamine 4-methyl-cyclohexylphenylamine p-amino phenylethylenediamine paminophenyl-3 -aminocyclopentylamine N- 3-hydroxycyclohexyl) -p-aminoaniline 4-cyclohexylaminecyclopentanol-3 N- (3 '-methylcyclopentyl l ,4-diaminocyclohexane 4,4-dicyclohexaneolylamine N- 3'-methylcyclohexyl) -4-aminocyclohexane N- (2'-hydroxycyclohexyl) -1,4-diaminocyclohexane The preparation of the reaction product compounds discussed hereinabove as suitable for addition to aqueous alkaline cyanide zinc plating baths in accordance with the present invention, is also disclosed in US. Patent No. 2,972,572 issued to R. P. Cope, J-r., et al. and assigned to the assignee of the present invention. It will be understood that substantially equimolar quantities actually take part in the reaction although other stoichiometry may be employed with less efiiciency.

The polyvinyl alcohol for use in this invention may be partially acetylated. It is preferred that the polyvinyl alcohol be about 2040% acetylated for ease of solubility in the resultant additive mixture. Low residual acetate polyvinyl alcohol resins require temperatures of 8595 C. (l85203 F.) to prepare resin solutions. A low molecular Weight resin is also preferred for ease and completeness of solution. This does not limit the kind of polyvinyl alcohol resin which may be used but only sets forth the preferred resin for this invention. It should be understood that the type or molecular weight of the polyvinyl alcohol is limited only by the solubility in the aqueous alkaline zinc cyanide electrolyte. .The polyvinyl alcohol employed must, of course, be soluble in the electrolyte. The polyvinyl alcohol may be used in combination with at least one reaction product or dithiocarbamate compound or with at least one reaction product and dithioc-arbamate compound.

The combination of polyvinyl alcohol with either the reaction product or dit-hiooarbamate compound, or with both, is incorporated into aqueous alkaline zinc cyanide plating baths as illustrated by the following specific examples:

Example IX OZ./ gal. Zinc oxide 5.6 Sodium cyanide 10.5 Sodium hydroxide 3.0 Polyvinyl alcohol 01 Reaction product of 2-thiohydantoin and ammonia 0.01

Bright zinc may be electrodeposited from this electrolyte in the range of from about 5 to about 50 amperes/ft. The plating will be semi-bright in the range of about 50 to about amperes/ftP. The color of the deposit will be whiter and more pleasing in appearance than the normal yellowish color.

Example X Oz./gal. Zinc oxide 5.6 Sodium cyanide 12.3 Sodium hydroxide 5.0

Polyvinyl alcohol 0.0 25 Zinc di butyldithiocarbamate 0.01

Bright zinc may be electrodeposited in the range of from about 2 to about 28 amperes/ft. A deposit more reflective than normal will be apparent above 28 amperes/ft Example XI Oz./gal. Zinc oxide 5.6 Sodium cyanide 12. 3 Sodium hydroxide 5.0 Polyvinyl alcohol 0.05 Reaction product of Z-thi-ohydantion and 2- anrinoethanol 0.1

Bright zinc may be electrodeposited from this electrolyte in the range of from about 5 to about 50 amperes/ft. The plating will be semi-bright in the range of about 50 to about 90 amperes/ftfi. The color of the deposit will be whiter and more pleasing in appearance than the normal yellowish color.

Example XII Oz./gal. Zinc oxide 5.6 Sodium cyanide 12.3 Sodium hydroxide 5.0

Polyvinyl alcohol 0.025 Zinc dimethyldithiocanb amate 0.1

Bright zinc may be electrodeposited in the range of from about 2 to about 28 amperes/ftfi. A deposit more reflec- Zinc that is bright and fair in color may be electrodeposited from this electrolyte.

Example XIV Oz./gal. Zinc oxide 5.0 Sodium cyanide 12.0 Sodium hydroxide 5.0 Polyvinyl alcohol 0.08 Zinc dimethyldithiocarbamate 0.02

Reaction product of 2-thiohydantoin and 2 aminoethanol 0.3

Zinc that is very bright with good color may be electrodeposited from this electrolyte. The brightness on the extreme low current density range will be particularly outstanding.

It is to be understood that the concentration of the brightening agents, either singly or in combination, is limited only by the solubility of the agents in the aqueous alkaline zinc cyanide plating bath. It is preferred that a minimum concentration of 0.0005 oz./ gal. of each agent added be maintained in the bath. LAS an upper limit, it is preferred that the maximum concentration of the reaction products be about 0.5 oz./ gal. and that the concentration of polyvinyl alcohol be limited to a maximum of about 0.1 oz./g-al. In the preferred electrolyte composition, t-he dithiocarbarnate compounds may be employed up to the limit of solubility.

The electrolyte may be conveniently prepared by adding a novel addition agent brightener composition comprising (A) polyvinyl alcohol and (B) the reaction product compound obtained by reacting substantially equimolar quantities of at least one compound having the nucleus with at least one compound selected from the group consisting of compounds having the formula wherein R is a radical selected from the group consisting of hydrogen, monovalent and divalent saturated substituted and unsubstituted aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms in which the substituents for the substituted hydrocarbon radicals are selected from the group consisting of NH and OH radicals, phenyl radicals, monovalent and divalent alicyclic radicals containing from 5 to 6 carbon atoms in the ring in which the substituents are selected from the group consisting of CH NH OH radicals and aminop-henyl radicals to an aqueous alkaline zinc cyanide plating bath prepared according to principles known in the art. For example, an addition agent brightener composition comprising (A) polyvinyl alcohol and (B) the reaction product compound obtained by reacting substantially equimolar quantities of the 2- thiohydantoin and Z-aminoethanol may be added to an aqueous alkaline zinc cyanide electrolyte to provide the concentrations described hereinabove.

An electrolyte may also be prepared by adding a novel addition agent brightener composition comprising (A) polyvinyl alcohol and (B) at least one dithiocarbamate cdmpound selected from the group consisting of compounds having the formulas Y R s s R and Where R is selected from the group consisting of monovalent and divalent saturated hydrocarbon radicals having from 1 to 4 carbon atoms and in which the substituents are selected from the group consisting of NH OH and COOR said R is selected from the group consisting of H, NH4 and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH CH NH (CH NH Na, K, C-a, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, to known aqueous alkaline zinc cyanide plating baths. For example, an addition agent composition comprising A) polyvinyl alcohol and (B) zince dirnethyldithiocarbamate may be added to an aqueous alkaline cyanide zinc bath to obtain the desired electrolyte.

An electrolyte may also be prepared by adding a novel addition agent composition, comprising (A) polyvinyl alcohol, (B) at least one described reaction product compound and (C) at least one described dithiocarba-mate compound to known aqueous alkaline zinc cyanide electrolytes.

For example, the novel composition comprising (A) polyvinyl alcohol, (B) a brightener compound obtained by reacting substantially equimolar quantities of 2-thiohydantoin and Z-aminoethanol and (C) zinc dimethyldithiocarbamate may be added to an aqueous alkaline zinc cyanide plating bath to obtain an electrolyte of this invention.

The electrodeposit produced with an aqueous alkaline zinc cyanide electrolyte containing polyvinyl alcohol together with either one or both of the reaction product compounds and dithiocarbamate compounds responds in an excellent manner to clear conversion coatings and dilute oxidizing bright dips. When subjected to a ten second dip in a clear conversion coating bath the deposits became brilliant and exhibited a pleasing blue white color.

It is to be understood that the zinc oxide, sodium cyanide and sodium hydroxide contents of the cyanide baths outlined hereinabove are only examples and that applicants invention is not to be limited by these specific cyanide bath compositions. For example, zinc cyanide may be employed in place of Zinc oxide with an appropriate reduction in the sodium cyanide content so that a proper cyanide-zinc ratio may be maintained. Other aqueous alkaline zinc cyanide compositions are known in the art and may be employed with the addition agent compositions of this invention.

While there have been shown and described what are presently considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific methods and compositions shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions and at least one brightener compound selected from the group consisting of compounds haviny the formulas where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of -NH -OH and -COOR and R is selected from the group consisting of H, NH, and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH CH NH (CH NH Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M.

2. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing Zinc ions and at least one brightener compound selected from the group consisting of compounds having the formulas Where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the 'substituents are selected from the group consisting of NH OH and -COOR and R is selected from the group consisting of H, NH; and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH CH NH (CH NH Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, said brightener being present in a concentration of at least 0.0005 ounces per gallon.

3. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions and at least one brightener compound selected from the group consisting of compounds having the formulas Where R is selected from the group consisting of monovalent .and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of NH OH and -COOR and R is selected from the group consisting of H, NH and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH CH NH (CH NH Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, said brightener being present in a concentration range of 0.003 to about 0.02 ounces per gallon.

4. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions and tetra methylthiuramdisulfide in a concentration of at least 0.0005 ounces per gallon.

5. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions and zinc dimethyldithiocarbamate in a concentration range of about 0.003 to about 0.02 ounces per gallon.

6. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions, polyvinyl alcohol and at least one brightener compound selected from the group consisting of compounds having the formulas and Where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of -NH OH and COOR and R is selected from the group consisting of H, NH, and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of 'NH CH NH (CH NH Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, said polyvinyl alcohol present in a concentration up to about 0.08 ounces per gallon and said brightener compound being present in a concentration of at least 0.0005 ounces per gallon.

7. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions, polyvinyl alcohol and at least one brightener compound selected from the group consisting of compounds having the formulaes where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of NH -OH and -QOOR R is selected from the group consisting of H, NH; and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH OH NH Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, said polyvinyl alcohol present in a concentration up to about 0.08 ounce per gallon and said brightener compound being present in a concentration range of 0.003 toa bout 0.0 2 ounce per gallon.

8. An aqueous alkaline zinc cyanide plating solution for electrodepositing zinc containing zinc ions, (A) polyvinyl alcohol, (B) a brightener compound obtained by reacting substantially equimolar quantities of at least one compound having the nucleus C N Y C [I I ll with at least one compound selected from the group consisting of compounds having the formula /R HN wherein R is a radical selected from the group consisting of hydrogen, monovalent and divalent saturated substituted and unsubstituted aliphatic hydrocarbon radicals having from 1 to 4 canbon atoms in Which the substituents 'for the substituted hydrocarbon radicals are selected from the group consisting of NH and OH radicals, monovalent and divalent alicyclic radicals containing from 5 to 6 carbon atoms in the ring in which the substituents are selected from the group consisting of -'CH N-H and OH radicals, phenyl radicals and aminophenyl radicals and (C) at least one brightener compound se- N-C-S- M where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of Ntl-I OH and COOR and R is selected from the group consisting of H, NH, and alkali metal salts, M is selected from the group of monovalent and divalent materials selected from the group consisting of NH4, 'CHgNHs, (CH3)2NH2, :Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, said (A) present in a concentration up to about 0.08 ounce per gallon, said 3) present in a concentration of from 0.0005 to about 0.5 ounce per gallon and said C) present in a concentration of at least 0.0005 ounce per gallon.

9. An addition agent composition suitable for introduction into an aqueous alkaline zinc cyanide electrolyte consisting essentially of (A) polyvinyl alcohol and (B) at least one brightener compound selected from the group consisting of compounds having the formulas and where R'is selected from the group consisting of monovalent and divalent saturated hydrocarbon radicals having from 1 to 4 carbon atoms and in which the substituents are selected from the group consisting of NH OH and COOR and R is selected from the group consisting of N, N H and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NI-IQ, CH3NH3, '(CH3)2NH2, Na, K, Ca, Zn, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M.

10. An addition agent composition suitable for introduction into an aqueous alkaline zinc cyanide electrolyte consisting essentially of '(A) polyvinyl alcohol, (B) a brightener compound obtained by reacting substantially equimolar quantities of at least one compound having the nucleus CN--C- [I H S with at least one compound selected from the group consisting of compounds having the formula wherein R is a radical selected from the group consisting of hydrogen, monovalent and divalent saturated substituted and unsubstituted aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms in which the substituents for the substituted hydrocarbon radicals are selected from the group consisting of NH and OH radicals, monovalent and divalent alicyclic radicals containing from 5 to 6 carbon atoms in the ring in which the substituents are selected from the group consisting of OH -NH and OH radicals, phenyl radicals and aminophenyl radicals and (C) at least one brightener compound selected from the group consisting of compounds having the formulas where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of NH OH and OOOR and R is selected from the group consisting of H, NH; and alkali metal salts, M is selected from the group of monovalent and divalent materials selected from the group consisting Of NI-I4, CH3'NH3, (OH3)2NH2, Na, K, Ca, 211, Mg, Cd, Ni, Fe, Co, M and Mn and n is equal to the valence of M.

11. An addition agent composition suitable for'introduction into an aqueous alkaline zinc cyanide electrolyte consisting essentially of (A) polyvinyl alcohol, (B) a brightener compound obtained by reacting substantially equimolar quantities of 2-thiohydantoin and 2-amino ethanol and C) zinc dimethyldithiocarbamate.

12. An addition agent composition suitable for introduction into an aqueous alkaline zinc cyanide electrolyte consisting essentially of (A) polyvinyl alcohol, (B) a brightener compound obtained by reacting substantially equimolar quantities of Z-thiobanbituric acid and aniline and (C) nickel diisopropyldithiocarbamate.

13. An addition agent composition suitable for introduction into an aqueous alkaline Zinc cyanide electrolyte consisting essentially of (-A) polyvinyl alcohol (B) a brightener compound obtained by reacting substantially equimolar quantities of l-acetyl-Z-thiohydantoin and diisopropyl amine and (C) tetraethylthiuram disulfide.

14. .A method of electrodepositing bright zinc metal comprising the steps of passing a current from an anode to a cathode to be plated in an aqueous alkaline zinc cyanide electrolyte containing zinc ions and at least one brightener compound selected from the group consisting of compounds having the formulas Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valance of M.

15. A method of electrodepositing bright Zinc metal comprising the steps of passing a current from an anode to a cathode to be plated in an aqueous alkaline zinc cyanide electrolyte containing zinc ions and (A) polyand 13 vinyl alcohol, ('B) a brightener compound obtained by reacting substantially equimolar quantities of at least one compound having the nucleus C-NC II I ll with at least one compound selected from the group consisting of compounds having the formula I wherein R is a radical selected from the group consisting of hydrogen, monovalent and divalent saturated substituted and unsubstituted aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms in which the substituents for the substituted hydrocarbon radicals are selected from the group consisting of -N H and -OH radicals, monovalent and divalent alicyclic radicals containing from to 6 carbon atoms in the ring in which the substituents are selected from the group consisting of -OH NH and OH radicals, phenyl radicals and arninophenyl radicals and (C) at least one brightener compound se lected from the group consisting of compounds having the formulas and where R is selected from the group consisting of monoyalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of -NH --OH and -COOR and R is selected from the group consisting of H, NH; and alkali metal salts, M is selected from the group of monovalent and divalent materials selected from the group consisting of NH CHgNHg, (OH3)2"NH2, Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M, said (A) present in a concentration up to about 0.08 ounce per gallon, said B) present in a concentration of from 0.005 to about 0.5 ounce per gallon and said (C) present in a concentration of at least 0.0005 ounce per gallon.

16. An aqueous alkaline Zinc cyanide plating solution for electrodepositing zinc containing Zinc ions and at least one brightener compound selected from the group consisting of compounds having the formula R s s R N-( DSS( JN where R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 t0 4 carbon atoms and the substituents are selected from the group consisting of NH OH and --OO=OR and R is selected from the group consisting of H, N-H and alkali metal salts.

17. An aqueous alkaline Zinc cyanide plating solution for electrodepositing Zinc containing zinc ions and at least one brightener compound selected from the group consisting of compounds having the formula wherein R is selected from the group consisting of monovalent and divalent saturated substituted and unsubstituted hydrocarbon radicals having from 1 to 4 carbon atoms and the substituents are selected from the group consisting of iN-H --OH and -COOR and R is selected from the group consisting of H, N11 and alkali metal salts, M is selected from the group of monovalent and divalent materials consisting of NH OH NH 2)2 2 Na, K, Ca, Zn, Mg, Cd, Ni, Fe, Co, Mo and Mn and n is equal to the valence of M.

References Cited by the Examiner UNITED STATES PATENTS 2,589,209 3/ L952 Kardos 20 455 X 2,740,754 4/ 1956 Hoffman l20-4--5 5 2,860,089 11/ 1958 Jackson 204 2,910,413 10/ 1959 Strauss et al 204-55 2,966,448 12/ 1960 Connor 20455 X 2,989,449 6/1961 Mackey et al. 204-55 3,018,232 1/1962 Bishofi et al 20=4-44 JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner.

G. KLAJPLAN, Assistant Examiner. 

1. AN AQUEOUS AKALINE ZINC CYANIDE PLATING SOLUTION FOR ELECTRODEPOSITING ZINC CONTAINING ZINC IONS AND AT LAST ONE BRIGHTENER COMPOUND SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS HAVING THE FORMULAS 